Process for making low alkali cement clinker

ABSTRACT

The potential K 2  O content of cement clinker due to the presence of potassium compounds in the raw feed mix is substantially eliminated by introducing an active agent into the kiln along with or in conjunction with the fuel used to fire the kiln. The active agent is effective to convert K 2  O to KCl and preferably is a chlorinated organic waste product burned along with the fuel.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 416,458,filed Nov. 16, 1973, now abandoned, and which is a continuation-in-partof abandoned application Ser. No. 311,898, filed Dec. 4, 1972, nowabandoned.

BACKGROUND OF THE INVENTION

In the manufacture of Portland cement, a factor which has assumedgreater importance in recent years is the control of alkali content inthe cement clinker. As is conventional in the art, what is meant byalkali herein is either Na₂ O or K₂ O. The presence of alkali in thecement clinker can result in what is known as the alkali-aggregatereaction, an effect which causes excessive expansive action of theconcrete and serious weakening of the structure involved.

Various techniques have been used to obtain low total alkali content ofthe clinker which may be classed as follows:

1. Raw material control.

A. The use of raw materials which are themselves of low alkali content.

B. Leaching soluble alkali salts from the raw materials themselves.

2. Flue dust recycle control.

A. Discarding the flue dust.

B. Leaching out soluble alkali salts from the flue dust prior torecycling it to the raw mix.

3. Process parameter modification

A. Increasing the temperature of the burning process.

B. Increasing the time period of the burning process.

C. Modifying the cooling process.

4. Raw mix additives.

An effective agent which has been found is CaCl₂.2H₂ O although to beeffective its use can be costly. Probably the most effective agentscurrently in use are those containing hydrochloric acid. i.e. certainpickling liquors. When calcium chloride dihydrate is used it is added tothe raw feed mix which, as is conventional, may be in dry or in slurryform. Likewise, hydrochloric acid when used is also added to the rawfeed.

Conventionally, the mix progresses to the hotter regions of the kilnwhere the organic matter burns away and the carbonates lose carbondioxide, a portion of the sulfates also is decomposed, liberating SO₃,and chloride and alkali salts are partially volitalized. It isprincipally in this region of the kiln, before a portion of the mass isconverted to liquid, where alkali loss is effected. It should be noted,in this respect, that even without the addition to the raw feed mix ofmaterial calculated specifically to reduce alkali content, one mayexpect on the average a loss of about 53% of the K₂ O and 19% of the Na₂O incidental to the burning process, reaching final values typicallyless than 1% of the clinker.

Significant reduction in alkali content by the use of raw feed mixadditives requires an economically significant amount of the additiveeven though the percentage amount of additive in the raw feed mix islow. This latter fact creates an additional problem in that theadditive, to be effective must be very uniformly dispersed throughoutthe mix and adequate control is difficult to achieve.

Nevertheless, the use of additives to reduce alkali content of theclinker is widely practiced if for no other reason than to meet the ASTMstandards for cement.

BRIEF SUMMARY OF INVENTION

The present invention relates to the discovery that the alkali contentof cement clinker may be significantly and surprisingly reduced byintroducing controlled amounts of an active agent into the kiln togetheror in conjunction with the fuel utilized to supply the kiln with thenecessary heat. Preferably, the active agent is a liquid chlorinatedorganic waste product in which case the active agent utilized may bediluted with a liquid non-chlorinated waste product so that the mixtureitself is a fuel having significant heat value which allows reduction inthe amount of conventional fuel used. However, the active agent need notbe in liquid form nor does it have to be an organic material. Solid,liquid or gaseous active agents may be employed so long as they arecapable of being broken up, dispersed or otherwise swept along throughthe kiln incidental to the combustion process so that the raw feed mixas it is being converted to clinker is maximally and as uniformly aspossible contacted so that substantially all of the potassium content ofthe raw feed mix is volatilized as KCl.

The invention may be practised by the addition of the active agent tothe fuel either in direct admixture therewith or as introduced incontrolled quantities with respect to the introduction of fuel, eitheralone, or in conjunction with conventional additives introduced into theraw feed mix.

DETAILED DESCRIPTION OF THE INVENTION

Although the exact mechanism involved according to the present inventionis not fully understood, it appears that the introduction of the activeagent in conjunction with the fuel not only creates a condition in whichthe aforesaid uniformity of action occurs but also may allow differentmechanisms to occur within different regions of the kiln, all to the endthat less additive appears to be necessary according to this inventionto obtain significant reduction in alkali content of cement clinker ascompared with the amount of feed mix additives required to achieve acorresponding reduction in alkali content of the clinker. A more uniformeffectiveness of the active agent appears to result in connection withthe present invention and this factor alone appears to contribute to theefficiency of the process.

Various factors should be taken into consideration in selecting theparticular active agent used in connection with this invention, amongwhich availability, cost and relative usefullness for other purposes arethe chief factors. One very significant advantage of this invention isthat many materials which otherwise are waste products whose disposalcreates a problem may be used advantageously. Thus, various wasteproducts from chemical processes may be used and many of them willrepresent readily available material with which to practise theinvention. However, the active agents herein are not limited to suchby-products for it is in general expeditious to utilize any active agentso long as it does not contain material which would be detrimental tothe cement making process or would create enviromental pollutionattendant upon its combustion, or would more usefully be employed foranother purpose. By "active agent" as used herein is meant any materialwhich when introduced with or in conjunction with the fuel for firingthe kiln is effective ultimately to convert the potassium content of theraw feed mix to KCl.

In general, however, a great many chlorinated organic waste productswill be available for use among which may be noted various saturated,unsaturated, aromatic, cyclic, heterocyclic or polymeric chlorinatedcompounds such as carbon tetrachloride and hexachloroethane;trichloroethylene and vinyl chloride; monochlorobenzene andpara-chlorotoluene; chlorocyclohexane and 3,3 dichloro- 1,2dimethylcyclopropane; 3,5 dichoropyridine and 2,6,8 trichloropurine;polyvinyl chloride and chlorinated polyethylene, as well as chlorinatedpesticides such as lindane and the DDT family. The above arerepresentative only.

Because many such chlorinated organic waste products are liquids, theiruse in admixture with and in controlled amounts in association with fueloil as conventionally utilized to fire the kilns of cement plants allowsa very precise control of the active agent addition according to thepresent invention.

Gaseous as well as solid materials may also be used, however, and theadvantages of this invention may be most pronounced when a useable wasteproduct is at hand which itself presents a disposal problem. Forexample, disposable PVC containers are in widespread usage for manydifferent products and when discarded may present a disposal problem.Such materials may readily be salvaged for use according to thisinvention.

If desired, conventional alkali content-reducing raw feed mix materialadditives may be employed in minor amount to achieve alkali contentreduction in the conventional way while further and enhanced alkalicontent reduction is achieved in the hot regions of the kiln by theactive agent concept according to the present invention.

EXAMPLE I

In a conventional calcining kiln for producing cement clinker, the rawfeed mix is a slurry including limestone, feldspar, iron oxide, alumina,and silica fed into the upper end of the inclined kiln. At the lower endof the kiln fuel oil and chlorinated liquid organic waste in conjunctiontherewith is fed at a rate sufficient to produce the heat necessary tocalcine and to fuse the raw feed mix and produce cement clinker which isdischarged at the lower end of the kiln. In the Example herein, the kilnwas about 500 feet long and the fuel is No. 6 oil preheated to about160° F introduced into the kiln at a rate of about 2000 gal/hr. Theactive agent is a mixture of 93% (by volume) of a by-product from themanufacture of chlorotoluenes and 7% of a by-product from themanufacture of carbon tetrachloride, the mixture containingapproximately 40% equivalent chlorine, trace free acidity of HCl, tracefree water and trace amount of free chlorine, and is introduced by aseparate nozzle with the fuel at the rate of about 80 gal/hr.Specifically, the by-product of the manufacture of chlorotoluenescontaines about 99% of chlorotoluene with minor amounts ofmeta-chlorotoluene and para-chlorotoluene, while the by-product of themanufacture of carbon tetrachloride contains about 94% carbontetrachloride, about 4% chloroform and about 2% of a mixture ofchlorinates including trichloroethylene, perchlorethylene, ethylenedichloride, tetrachloroethane, pentachloroethane and hexachloroethane.This example represents one mode of practising the invention wherein theactive agent contributes but a small precentage of the BTU required tomake the cement clinker.

Analysis of typical Portland cements which may be obtained according toExample I are as follows:

    ______________________________________                                                Type I                                                                              Type II Type III Type IV White                                  ______________________________________                                        Loss on Ignition                                                                         1.3%    0.8%    1.2%   0.9%    0.9%                                SiO.sub.2  21.3    22.3    20.4   24.3    25.0                                Al.sub.2 O.sub.3                                                                        6.0     4.7     5.9    4.3     3.4                                  Fe.sub.2 O.sub.3                                                                        2.7     4.3     3.1    4.1     2.8                                  CaO        63.2    63.1    64.3   62.3    64.1                                MgO       2.9     2.5     2.0    1.8     1.9                                  SO.sub.3  1.8     1.7     2.3    1.9     1.0                                  K.sub.2 O --      --      --     --      --                                   ______________________________________                                    

EXAMPLE II

In this example, the same conditions are present as set forth above inExample I except that the active agent is diluted to a chlorine contentof about 2% by mixing the active agent with a non-chlorinated wasteproduct having a BTU content per gallon essentially the same as the 6fuel oil.

To obtain the same rate of heat input and of equivalent chlorineintroduction into the kiln as in Example I, the fuel oil flow rate isreduced to about 500 gallons/hour while the rate of diluted active agentis about 1600 gallons/hour, the specific BTU content of the active agentplus diluent being about equal to that of the fuel oil. Thus,significant reduction in fuel oil consumption is realized. At the sametime, the increased flow rate of active agent source allows a moreprecise control of the introduction of equivalent chlorine into thesystem.

As noted above, various chlorinated organic waste products may be usedand, as diluents as in Example II, various waste products having highheat content may be employed.

Large quantities of chlorinated organic wastes are generated in theproduction of chlorinated organic compounds and, if left untreated,constitute pollutants contaminating and endangering the naturalresources of our environment. Morover, these chlorinated organic wastescan be hazardous to animal and human life. Also, the finished productsformed or chlorinated organics, which are widely distributed forindustrial, agricultural and domestic use, frequently are not completelyconsumed or destroyed during their usage and remain stable to furthercontribute to environmental pollution. Accordingly, the disposition andmanagement of these chlorinated organic wastes are serious problems inthe field of environmental control.

The chlorinated organic wastes are generated either from the operationsinvolved in the production of chlorinated organic compounds or from thefinished products themselves after they have served their usefulfunction, or from contaminated or rejected finished products.

For example, in the production of desired chlorinated organic products,certain side reactions occur which yield unwanted chlorinated compoundsconsidered to be wastes. Frequenctly, multiple reactions are conductedin an effort to obtain the desired product, each of these reactionsresulting in wastes containing chlorinated materials, the chlorinecontent often being significantly large.

Also, significant amounts of chlorinated organic wastes are generatedfrom the chlorinated organic finished products used in domestic,industrial and agricultural applications. For example, specificindustrial wastes include the many chlorinated solvents used for thecleaning and degreasing of metal parts and the chlorinated liquidsemployed in power transformers and capacitors. Domestic and agriculturalchlorinated organic wastes include weed killers, pesticides and the likewhich have not been entirely consumed, have become spoiled orcontaminated, or have been banned from use by law.

However, many other active agents may be used as, for example, chlorinegas, calcium chloride, silicon tetrachloride, etc.

An important consideration in connection with this invention is that theactive agent is introduced into the kiln along with or in conjunctionwith the main fuel source for firing the kiln. In this way, the activeagent is immediately acted upon by the intense heat of the flame, iswell dispersed or distributed throughout the cross section of the kilnand is swept along with the combustion gases. In this way, the activeagent comes into contact with the feed material throughout the kiln andwill also maximally contact the feed material in the preheaters asconventionally employed. This is in direct contrast to the use of rawfeed mix additives. For example, when calcium chloride is used as a feedadditive, the following reaction:

    CaCl.sub.2 + K.sub.2 O →CaO + 2 KCl

does not occur until the temperature of the material exceeds about 1800°F. Similarly, when spent pickling liquor containing HCl is used as theraw feed mix the HCl first reacts with the limestone to form CaCl₂ andthe aforesaid reaction thereof with K₂ O does not occur until thetemperature exceeds about 1800° F.

With the present invention, a uniformly distributed formation of CaCl₂may take place in the cooler regions of the kiln or in the preheaterwhen a chlorinated organic waste is used due to reaction of HCl withlimestone, but conversion of K₂ O to KCl is not restricted to thisparticular procedure because of the essentially continuous contactsbetween the active agent and the material throughout the kiln. Whenmaterials such as calcium chloride are employed as the active agentherein, their uniform distribution and the sweeping thereof through thekiln also assures, as before, an efficient and uniform action upon theraw feed mix before and as it is being converted to the cement clinker.

What is claimed is:
 1. The method of making cement clinker, whichcomprises the steps of:a. forming a raw feed mix which when calcinedwill produce cement clinker having an unacceptably high value of K₂ Oalkalinity; b. continuously introducing the raw feed mix of step (a)into one end of a kiln while recovering cement clinker from the otherend of the kiln; c. firing the kiln with a fuel at a rate sufficient toproduce the cement clinker; and d. controlling the K₂ O alkalinity ofthe recovered clinker by incorporating a chlorinated organic liquid fuelas part of the fuel employed to fire the kiln in step (c), said organicliquid fuel being incorporated in amount sufficient significantly toreduce the K₂ O alkalinity of the recovered clinker.
 2. The method asdefined in claim 1 wherein the chlorinated organic fuel of step (d) is awaste product containing o-chloro toluene.
 3. The method as defined inclaim 1 wherein the chlorinated organic fuel of step (d) is a wasteproduct containing a mixture by volume of 93% o-chloro toluene and 7%carbon tetrachloride.
 4. The method as defined in claim 1 including thestep of adding a chlorine-containing compound to the raw feed mix ofstep (a) in amount sufficient to reduce the K₂ O alkalinity of therecovered clinker.
 5. The method as defined in claim 2 including thestep of adding a chlorine-containing compound to the raw feed mix ofstep (a) in amount sufficient to reduce the K₂ O alkalinity of therecovered clinker.
 6. The method as defined in claim 3 including thestep of adding a chlorine-containing compound to the raw feed mix ofstep (a) in amount sufficient to reduce the K₂ O alkalinity of therecovered clinker.